Radiotelegraphy transmission system



June 3', 1 2 1,496,214

L. F. FULLER ET AL RADIOTELEGRAPHY TRANSMISSION SYSTEM Filed May 22 1919 WITNESS IN V EN TORS who} ATTORNEYS T E S P TNr orrlclz. 7

LEONARD F. FULLER AND HAROLD F. ELLIOTT. OF PALO ALTO, CALIFORHIA, AS-

SIGNORS, BY MESNE ASSIGNMENTS, TO FEDEBIAI: TELEGRAPH COMIPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALIFORNIA. i

B-ADIOTELEGRAPHY TRANSMISSION SYSTEM.

Application filed May 22,

T 0 all whom it may concern:

Be it known that WQ$LEONARD F. FULLER and HAROLD F. ELLIOTT, citizens of the United States, and residents of Palo Alto, county of Santa Clara, and State of California, have invented a certain new and useful Radiotelegraphy Transmission System, of which the following is a specification.

The invention relates to radio telegraphy transmission systems and particularly to a system employing an arc radio generator of the Poulsen type.

An object of the invention is to signal without the use of the so-called compensating wave.

Another object of the invention is to provide a signaling system in which the current a in the antenna circuit is reduced to zero,

without varying the load on the arc radio generator.

A further object of the invention is to provide a signaling system in which the kilovolt-amperes (Kva) which the signaling in the claims, may be embodied in a strument must handle are reduced to a minimum.

The invention possesses other advan tageous features, some of which, with the foregoing, willrbe set forth at length in the following description where we shall outline in full those embodiments of the invention which we have selected for illustration in the drawings accompanying and forming part of the present specification. In said drawings we have shown several different forms of our invention, but it is to be understood that we do not limit ourselves to such forms, since the invention, as expressed in plurality of forms.

Referring to said drawings:

Figure 1 is a diagrammatic representation of the system of our invention employing a double contact switching device.

Figure 2 is a similar representation of a modified form of the system.

Figure 3 is a similar representation of a modified form, showing a single contact switching device.

Figure 4 is a similar representation showing a modified form of signaling device.

Figure 5 is a similar representation showing a modified form of circuit.

This invention provides for signaling 1919. Serial No. 298,909.

without the use of the compensating wave, by allowing current in the transmitting antenna only during the periods of dots and of a definite switching arrangement which renders it impossible for the current to exist in the antenna when it is not desired, as contrasted with well known absorbing circuit methods, wherein current may be maintained in the antenna or switched into a local absorbing circuit by reason ofthe special and peculiar characteristics of the are converter. In United States Patent No. 1,306; 223, issued to L. F. Fuller, an absorbing circuit system is shown. In the present system, the peculiar characteristics of the are are not relied upon and the antenna current is reduced from maximum to zero, by short circuiting the source of inphase E. M. F. in the circuit, and this is accomplished without varying the load on the arc converter and consequently without varying the load on the D. G. generator feeding the arc. The signaling device is inserted in the circuit at a point at which the power factor of the current and voltage is practically unity and consequently the load on the switching device is a minimum. One way in which it is possible to accomplish this result is by locating a part of the circuit that replaces, during the periods of no radiation, the antenna circuit, directly in series with this antenna circuit. This part of the circuit con sists entirely of inductive and capacitive reactance neutralizing each other, or tuned to the frequency of the system. Thus, the total effect of this part of the circuit on the antenna circuit is negligible and across the terminals of the inductance and capacity a minimum potential difference is obtained for currents of the correct frequency. By

proper arrangement of a resistance or other consumer of energy and a switching means, the substitute circuit can then be made to have substantially the same characteristics as the antenna circuit, so that the load on the source remains the same, independent of choice of paths.

The system disclosed in Figure 1 com prises an arc converter 3 of the Pouls'en type which is fed with direct current fronr the generator 1 through the combined magnet winding and choke coil 2, one side of the are being grounded. Connected to the are 3 is a circuit containing a variable radio frequency inductor 41, a radio frequency capacitance 5, a variable radio frequency resistor 6 and a suitable switch device. The switching device in this instance comprises two fixed contacts 10 and 11 and a movable contact 12 which is movable into engagement with either contacts 10 or 11. Contact 10 is connected to the circuit between the capacitance 5 and resistor 6 and contact 11 is connected to earth and to the earthed side of the arc. Movable contact 12 is connected to the resistor 6 and to the antenna circuit, comprising the variable radio frequency inductor 7 and the radiating antenna 8. When contacts 10 and 12 are in engagement, the arc oscillates on the antenna circuit, and when in this position, signals are transmitted. When contacts 11 and 12 are in engagement, the source of inphase E. M. F. is short circuited and no current exists in the antenna.

The resistor 6 is so adjusted that the radio frequency current delivered by the arc remains constant whether current is delivered to the antenna or circulates only in the local circuit. In practice, adjustments are made as follows,contacts 11 and 12 are brought into engagement and the arc is allowed to oscillate on the local circuit. The inductor 4 is then varied to make the wave length of the local circuit equal to that which it is desired to radiate from the antenna. Contacts 10 and 12 are then brought into engagement, causing current to flow into the antenna, and inductor 7 is then varied until the chosen wave length is obtained.

The reading of the radiation ammeter 13 in the circuit is then noted and the local circuit is again closed. The resistor 6 is then varied until the reading of the amnaeter is the same as when current was in the antenna. Signaling may now be accomplished by moving contact 12 alternately into engagement with contacts 10 and 11 without causing variation of the radio frequency current delivered by the are, thereby imposing a constant load on the D. C. gen erator. I

' The reactive drop across the inductor 1 is equal and opposite to the reactive drop across the capacitance 5 and all the voltage that the switching device must handle is the inphase driving E. M. F. The product of current and volts at the switching device is a minimum and the power factor is unity. The circuit consisting of inductive reactance 1, capacitive reactance 5, and resistance 6. serves as a substitute during the period of "no radiation for the antenna circuit; since by the adjustments it is made to have the same characteristics as the antenna circuit, the choice of either circuit does not affect the load supplied by the system.

In the system shown in Figure 2, the contact 10 is directly connected to one side of the are, and the circuit containing the inductor 1, capacitance 5 and the resistor 6, connects the same side of the arc with the antenna. By moving the key contact 12, the antenna may be directly connected to the arc, short-circuitin the inductor, capac itance and resistor, so that their losses do not reduce the antenna current. \Vhen the contacts 11 and 12 are in engagement, the source of inphase E. M. F. is short circuit-ed through the resistor-induetor-capaeitance circuit.

In the arrangement. shown in Figure 3, the position of the resistor 6 in the circuit is changed occurring between the earthed arc electrode and the signaling key 14 which in this instance comprises only two contacts, 15-16. In this arrangement it is necessary to slightly detune the antenna circuit. i. e., when the arc is delivering current to the antenna, the wave length must be slight ly different from that when it is oscillating on the local circuit only. This is necessary since otherwise the R I drop across the resistor 6 when tie key is closed would produce an E. M. F. which would set up current in the antenna. By slightly detuning the antenna circuit. this hangover current is reduced to a minimum, because the frequency of the E. M. F. caused by the P I drop in the resistor is slightly different from the resonant frequency of the antenna. A resistor 17 of high resistance may be shunted around the key contacts to reduce sparking in the well known manner. Instead of employing a moving contact key for varying the resistance of the circuit to the radio frequency current, as shown in Fig. 3. a non-rnoving contact device may be used, such as is shown in Fig. 4. This device itself is described in the afore-mentioned Fuller patent and is known as a hysteresis key. When the polarizing D. circuit of the key 23 is open, the resistance of the local circuit is high and current flows in the antenna circuit. When the polarizing circuit is closed, the polarizing current causes a reduction in the resistance of the local circuit. so that current flows in it and not in the antenna. To accomplish this, the antenna circuit is slightly detuned, as set forth hereinbefore.

In Figure 5 we have shown a'further modified arrangement of the system, in which short circulating is accomplished by a resonant circuit, consisting of the inductor 18 and the capacitance 19, of such values that the frequency remains the same whether the arc oscillates on the antenna or through the closed circuit.

This short circuit may 1 be 'reduced'by the detuning produced, by varying the inductor 18. Thismay be accomplished by any of; several well known methods, and we have chosen for illustration a key 21, short circuiting a few of the turns of the inductor 18.

The reason why current flows in the antenna circuit when the short circuiting resonant circuit is detuned is because the LC product of inductor 4; and capacitance 5 is the same as that of the antenna circuit proper, consisting of inductor 7 and capacit nce 8, audit inductor land capacitance 5 are considered as forming a frequency sifter, then energy will arrive at point 0, Figure 5, at this resonant frequency. The antenna circuit provides a resonant path for it, whereas the inductor-18-,capacitance-l9 path is non-resonant; hence the current flows in the antenna. Still another way of considering the matter is that by means of the LC interposed next to the arc, the latter is made a source'of constant frequency, like a radio frequency alternator, thus with these connections the arc converter can deliver radio frequency energy in quantity only at the frequency set by the frequency sifter.

We claim:

1. A radio telegraph-y transmission system, comprising a source of radio frequency current, an antenna circuit, a circuit containing an inductor and capacity connecting the antenna circu-itwith one side of said source, and a signaling device connected to earth at the point of minimum voltage of the radio frequency system.

2. A radio telegraphy transmission sys tem, comprising a source of radio frequency current, an antenna circuit, a local circuit containing inductance and a capacitance connecting the antenna circuit and said source and a signaling device arranged in the local circuit at a point of unity power factor.

3. A radio telegraphy transmission sys tem, comprising a source of radio frequency current, a local circuit containing inductance and a capacitance connected to said source, an antenna connected to the local circuit so that the inductance and capacitance are interposed between one side of the source and the antenna, and means for closing and opening the circuit between the antenna and the other side of the source.

4:. A radio telegraphy transmission system, comprising a source of radio frequency current, a local circuit containing inductance and a capacitance connected to said source, an antenna connected to said circuit, and means for closing said circuit whereby the source of inphase electromotive force of the antenna is short circuited and the antenna current reduced from maxium to zero, while maintaining the load on the said source substantially constant,

5 A radio telegraphy transmission sys tem comprising a source of radio frequency current earthed on one side, a local circuit containing inductance and capacitance connected to said source on the unearthed side, an antenna circuit connected to said local circuit so that said inductance and capacitance are interposed between the unearthed side of said source and the antenna circuit, and a switching device interposed between the connection to the antenna circuit and the earthed side of the source. I

6. A radio telegraph-y transmission system comprising a source of radio frequency current, a load circuit, reactors connected in series to the load circuit but having no appreciable effect upon the load supplied, an energy absorbing device so, arranged that it may be connected in series to the reactors, and means for causing said device to be sup,- plied with energy fromthe source through the reactors, whereby the load currentmay be stopped. I i

7. A radio telegraphy transmission system comprising a source of radio frequency current, a load circuit, capacitive and inductive reactors connected in series with the load circuit, but so tuned'that they have no appreciable effect upon, the load supplied to the load circuit, an energy absorbing-device arranged for series connection with the reactors, and. means for causing said device, to absorb energy from the source, whereby the load current isstopped, the device 'bei-ngso adjusted that the load supplied to it is subalstaitially equal to that supplied to the useful 8. A radio telegraphy transmission system comprising a source of radio frequency current, an antenna circuit, a local circuit having the same characteristics as the antenna circuit, that portion of the local circuit being in series with the antenna circuit which corresponds to the inductance and capacity of the antenna circuit, and means for render-' ing the remainder of the circuit active or inactive, whereby the antenna radiations may be stopped or continued.

9. A radio telegraphy transmission system comprising an arc radio generator having one side earthed, an antenna, an inductance and a capacitance interposed between and connecting the antenna with the unearthed side of the generator, a conductor connected to the earthed side of the generator and forming with said inductance and capacitance a local circuit, a resistor in said circuit, and means for intermittently allowing current in antenna by opening and closing the local circuit.

10. In a radio telegraphy transmission system, means for producing radio frequency oscillations, a radiating circuit connected to the source, a local circuit having an inductance and a capacitance connected in series with the source, the inductance and capacitance being substantially the equivalent of the inductance and capacitance of the radiating circuit, and means connecting between the radiating circuit and the local circuit for switchingcurrent into and out of the radiating circuit.

11. In a radio telegraphy transmission system, means for producing radio frequency oscillations, a radiating circuit connected to the source, a local circuit having an inductance and a capacitance connected in series with the source, the inductance and capacitance being substantially the equivalent of the inductance and capacitance of the radiating circuit, means connecting between the radiating circuit and the local circuit for switching current into and out of the radiating circuit, and means whereby the load on the source is maintained substantially constant for both active and inactive conditions of the radiating circuit.-

12. In a radio frequency transmission system having a load circuit for radiating energy, means for producing high frequency oscillations connected to said circuit, means for causing the potential drop across two points in the load circuit to be a minimum for currents at a definite frequency, and a circuit across the two points.

13. In a radio frequency transmission system having a load circuit for radiating energy, elements arranged in series included in the load circuit so proportioned relatively that there is a minimum potential difierence between the two points corresponding to the terminals of the elements in series for currents having substantially the frequency which it is desired to use, and a circuit connected to these points.

1.4. In a radio frequency transmission system having a load circuit for radiating energy, means for producing high frequency oscillations connected to said circuit, means for causing the potential drop across two points in the load circuit to be a minimum for currents at a definite frequency, and a circuit having resistance connected across the two points.

15. In a radio frequency transmission system having a load circuit for radiating en ergy, elements arranged in series included in the load circuit so proportioned relatively that there is a minimum potential diiference between the two points corresponding to the terminals of the elements in series for currents having substantially the frequency which it is desired to use, and a circuit having resistance connected across the two points.

In testimony whereof, we have hereunto set our hands at Palo Alto, California, this l3th day of May, 1919.

LEONARD FQFULLER. HAROLD F. ELLIOTT. In presence of- MARY H. BULEN, THELMA M. Knox. 

